Commercialized, low C-SWAP (Cost, Size, Weight and Power), software defined communications apertures will substantially increase network capacity in future wireless networks (e.g., 5G wireless networks). Embodiments of the present invention provide methods and systems that employ high gain, electronically steerable antennas for small cell radio access networks, backhaul, and millimeter wave applications. The steerable beam functionality may provide elevated data rates, reduced power consumption, spectrum reuse, and dynamic network reconfiguration. Additionally, network operating costs may be reduced and deployment schedules may become more flexible.
Future wireless network deployments (e.g., 5G wireless network deployments) are expected to offer increased data throughput over current deployments. From 2010 to 2020, industry expects mobile network traffic to increase by three orders of magnitude [1]. 5G wireless systems will incorporate a number of new technologies in order to meet the demands of spectrum crunch and energy consumption. Researchers and industry have proposed massive MIMO (multiple input multiple output) [2], cognitive radio [2], visible light communications [2], network densification [1], offloading [1], expanded and more efficient spectrum use [1], neighborhood small cells [3], millimeter wave backhaul [3], cloud radio access networks [3], coordinated multipoint processing [3] and native machine to machine support [4] as possible candidates for inclusion in 5G standards.
Presently, wide area or even omnidirectional antennas saturate spectrum due to their low directivity. Using low directivity antennas fundamentally leads to a higher energy cost per bit transmitted as the overwhelming majority of the radiated power is not captured by the receiving antenna unit. In addition, low directivity antennas spectrally pollute their coverage area, preventing similar antenna systems from operating simultaneously at the same frequency. Increasing network capacity then depends on moving to ever smaller cellular coverage areas to optimize the reuse of a carrier's very expensive spectrum.
Using high directivity antenna systems provides higher data rate per watt (due to SINR gains) by restricting the RF illuminated area. Spatial and angular diversity provide a potentially significant increase in the network throughput by maintaining good ‘spectral hygiene’ and not radiating energy in unneeded directions. This leaves the area free for spectrum reuse by other antennas, pushing the overall system back towards noise limited rather than interference limited. It is possible to use a massive arrangement of non-scanning, high directivity, fixed antennas to cover a region. However, a substantial number of fixed antennas would be needed to assure coverage, which would be expensive and bulky. Gimbal mounted antennas are another possible steering beam option. However, they are likely to be far too slow, bulky and expensive to address multiple users within the coverage area adequately.
In contrast to static antennas, electronically steered apertures can reconfigure the radiation pattern in short time intervals (e.g., microseconds) to best service the customers within the antenna's coverage area. Embodiments of present invention includes methods and systems that employ steerable antennas for high directivity and fast electronic beam switching which we refer to as Directivity on Demand (DoD). A DoD operating mode reduces the deployed tower site density by exploiting the antenna's increased coverage range. Even for short range links, operators concerned about base station power consumption may find substantial energy savings when using high directivity antennas in addition to providing extended battery life for user equipment [5].
Adjacent cell towers can coexist using Inter-Cell Interference Coordination (ICIC) techniques to assure their beams act cooperatively and not interfere. Multipath noise is reduced as the physical channel is not distributed in unneeded directions. Non-line-of-sight (NLoS) communications could scan the beam to locate effective channels. Nomadic hotspots such as trains and ships can be served with a high gain link from a steered beam antenna. With sufficiently low cost steerable antennas, MIMO support can be enabled with separate apertures (or multiple feeds for one aperture) to achieve orthogonal space division multiplexing (OSDM).
Software defined apertures (SDAs) have been realized by Active Electronically Steered Arrays (AESAs) for decades [6]. AESAs have frustrated many attempts to reduce their cost, size, weight and power (C-SWAP) and continue to see almost exclusive use in the military domain. Despite the C-SWAP limitations, a number of groups have proposed phased array based solutions for next generation networking [3] [7] [8] [9].
Embodiments of the present invention utilize an alternative scanning beam technology that leverages surface scattering techniques to achieve robust beamforming. In antennas based on surface scattering techniques, coupling between a guided wave and propagating wave is achieved by modulating the electromagnetic properties of a surface in electromagnetic contact with the guided wave. This controlled surface modulation may be referred to as a “modulation pattern” or a “hologram pattern.” The guided wave in the antenna may be referred to as a “reference wave” or “reference mode” and the desired free space propagating wave pattern may be referred to as the “radiative wave” or “radiative mode.”
Surface scattering antennas are described, for example, in U.S. Patent Application Publication No. 2012/0194399 (hereinafter “Bily I”), with improved surface scattering antennas being further described in U.S. Patent Application Publication No. 2014/0266946 (hereinafter “Bily II”). Surface scattering antennas that include a waveguide coupled to adjustable scattering elements loaded with lumped devices are described in U.S. Patent Application Publication No. 2015/0318618 (hereinafter “Chen I”), while various holographic modulation pattern approaches are described in U.S. Patent Application Publication No. 2015/0372389 (hereinafter “Chen II”). Surface scattering antennas that include a waveguide coupled to adjustable slot elements are described in U.S. Patent Application Publication No. 2015/0380828 (hereinafter “Black I”). Curved or conformal surface scattering antennas are described in U.S. Patent Application Publication No. 2015/0318620 (hereinafter “Black II”). Broadband surface scattering antennas are described in U.S. Patent Application No. 62/271,524 (hereinafter “Black III”). All of these patent applications are herein incorporated by reference in their entirety, and shall be collectively referred to hereinafter as the “MSAT applications.”
Because surface scattering antennas utilize a holographic principle of controlled scattering of a reference wave off of a hologram defined by the antenna modulation pattern, surface scattering antennas will be equivalently and interchangeably described as “holographic beamforming antennas” through this specification. Whenever embodiments contemplate a beamforming antenna, it is contemplated that the beamforming antenna can be a holographic beamforming antenna or surface scattering antenna such as any of those disclosed in the above MSAT applications; and whenever embodiments contemplate configuring or adjusting a beamforming antenna, it is contemplated that the antenna can be configured or adjusted as disclosed as in any of the above MSAT applications.
Surface scattering antennas have been demonstrated to operate over a wide range of microwave and mmW frequencies, including frequency ranges from L band to V band (1-60 GHz). Surface scattering antennas can be rapidly reconfigured (e.g. in microseconds) to steer a beam in arbitrary directions or form different beam shapes in software (see, e.g., Chen II). Some approaches leverage traditional circuit manufacturing technologies for low cost and power consumption. Surface scattering antennas do not require discrete phase shifters or custom monolithic microwave integrated circuits (MMICs) but can instead leverage commercial off the shelf components developed for high volume production by the wireless industry. Unlike an AESA, a surface scattering antenna does not require distributed amplification and cooling, and this can substantially reduce the size, weight, complexity and power consumption for embodiments of the present invention.
Embodiments utilize surface scattering antennas that can be made conformal (see, e.g., Black II) to support more discrete deployment locations in municipalities that have stringent aesthetic requirements for antenna installations. In some embodiments the antenna profile thickness is as low as ½ inch (12.7 mm) which allows deployment in a variety of locations without disturbing the appearance of the host structure. It has been noted that spatial densification is likely to require this kind of low cost, low profile and conformable technology for discrete deployments [3].
Steerable high directivity antennas result in greater spectral reuse to minimize interference. For example, replacing a low directivity antenna on a small cell with a holographic beamforming antenna, while keeping a low directivity antenna on the UE, enhances the link margin compared to a link where both antennas have low directivity. The increased gain of a holographic beamforming antenna allows the UE to decrease its transmission power for UE while maintaining a good margin, increasing UE battery life and decreasing interference with other devices.
In much the same way that the advent of MIMO caused a redesign of the wireless protocol stack, so too will the use of SDAs for highly directive spatial channelization. No longer will the antenna be relegated to the less sophisticated PHY layer as traditionally has been the case. “Dumb” antennas were static elements and not used as an additional tool to increase throughput, spectral efficiency or range. SDAs represent the last dynamic piece of a fully software defined radio system and as such, will need a reshaped wireless protocol stack to inform the network on how best to take advantage of this new capability.
Some embodiments provide for using holographic beamforming antennas for adaptive routing within communications networks, such as wireless backhaul networks. For example, in future 5G networks, wireless backhaul will be employed to connect small cells. The small cells are unlikely to have dedicated fiber or wired links due to the predicted density of their deployment. These links will likely need beam steering for dynamic routing around obstacles and maintaining link performance in the presence of pole sway.
Further embodiments provide for using holographic beamforming antennas for discovering and/or addressing nodes in a communication network with steerable, high-directivity beams. For example, in future 5G networks, the macro cell, small cell and UE will be simultaneously engaged with each other, a concept which has been discussed as the heterogeneous network (HetNet) [11]. Both backhaul networks and radio access networks (RANs) may utilize high directivity beam steering and millimeter wave connectivity to end users to provide greatly expanded channel capacity.
Still further embodiments provide for using beamforming antennas to extend the range of communications nodes and to provide bandwidth assistance to adjacent communications nodes via dynamic adjacent cell assist (DACA). For example, in future 5G networks, small cells may be employed within the coverage area of a macrocell to divide the coverage into ever smaller subunits. Embodiments could reduce the number of needed small cells through Dynamic Adjacent Cell Assist (DACA).
Still further embodiments provide for using MIMO in concert with holographic beamforming for additional channel capacity. MIMO is enhanced by use of coordinated holographic beamforming antennas. The channel capacity of directed-beam MIMO scales linearly with the number of antennas and logarithmically with antenna gain. Networks can simultaneously utilize both MIMO and DoD (Directivity on Demand via holographic beamforming) to maximize channel capacity.
The foregoing summary is illustrative only and is not intended to be in any way limiting. In addition to the illustrative aspects, embodiments, and features described above, further aspects, embodiments, and features will become apparent by reference to the drawings and the following detailed description.